It is known that the freezing of such French straws requires following a freezing process defining a temperature kinetics in order to cool the biological substance to a negative temperature below its glass transition zone.
This temperature kinetics is made possible by the implementation of a first phase called equilibration phase and a second phase called freezing phase, which can be divided into several freezing sub-phases.
For example, the French straws are arranged at a temperature of the order of +4° C. for a first specific period, for example a few hours, for resting. This is the equilibration phase. Then, the French straws are subjected to a first drop in temperature, firstly from +4° C. to −10° C. in steps of the order of −5° C./min; then a second drop in temperature from −10° C. to −140° C. in steps of the order of −40° C./min. These are respectively the first and second freezing sub-phases comprised by the freezing phase.
The kinetics disclosed above is specified in the case where the filling phase is carried out at ambient temperature.
It will be observed that the temperature kinetics depends on the phase of filling the French straws since in fact, the implementation of this kinetics differs depending on whether this filling phase is carried out at ambient temperature or at a temperature below ambient temperature.
In the case where the French straws are filled at a temperature of the order of +4° C., the equilibration phase is then not necessary and the French straws are directly introduced into a freezing system.
In order to achieve such kinetics, it is necessary to have a filling system and a freezing assembly comprising in particular several freezing systems (or a freezing system provided with several cold zones) and optionally an equilibration system.
Generally, in order to be filled, the French straws are arranged horizontally and in ordered manner, i.e. arranged flat, in specific grooves arranged on a mobile conveyor. These grooves are shaped so that they can receive a particular type of French straws in order that the latter are arranged homogeneously.
After the French straws have each been filled with a certain volume of biological substance at ambient temperature, they are extracted from the grooves on the conveyor of the filling machine and are introduced into plastic boxes, which are themselves also shaped so that the French straws are aligned side by side each other, i.e. arranged homogeneously. These boxes are placed in an equilibration zone to rest. Then, the French straws are extracted from the plastic box to be introduced into freezing systems.
In the case where the French straws are each filled with a predetermined volume of biological substance at a temperature of the order of +4° C., they are then extracted from the grooves on the conveyor of the filling machine and are directly introduced into freezing systems.
These freezing systems are generally in the form of a conventional freezer in which racks are arranged horizontally, which are provided with locations intended to receive in an ordered manner French straws each previously filled with a certain volume of biological substance. As a variant, each French straw is introduced into a specific cylindrical or hexagonal tube, some (a predetermined number) of these cylindrical or hexagonal tubes are introduced into and arranged in a beaker and several beakers are arranged vertically and stacked inside a canister that is itself arranged vertically in the freezer.
From the American patent U.S. Pat. No. 4,227,381 a system of freezing is also known, in particular of French straws filled with biological substance, provided with a cooling enclosure passed through by a flow of cooling agent entering this chamber by an inlet duct and leaving this enclosure by an outlet duct. This enclosure has an internal space into which is introduced a single container having a plurality of conditioning cases arranged in an ordered manner, i.e. aligned side by side and stacked, inside the container. In each conditioning case is arranged a French straw or an ampule previously filled with a volume of biological substance to be frozen.
The container, the cases introduced into this container as well as the French straws or ampules each filled with a volume of biological substance and introduced into these cases are arranged in the cooling enclosure in a direction similar to that defined between its inlet connector and its outlet connector.
The system is moreover provided with a unit for driving the cooling enclosure in rotation on itself. For this, the cooling enclosure is in mechanical inter-engagement allowing the driving in rotation at the level of its inlet connector. This cooling enclosure is also in mechanical inter-engagement allowing the rotation at the level of its outlet connector, which outlet connector is connected to an outlet duct for the flow of cooling agent.
In order to freeze the French straws, the cooling enclosure is set in rotation on itself and the flow of cooling agent flows along the closed container which comprises the cases each containing a French straw. The French straws are therefore driven in rotation whilst being held in the cases, which are held in the single container.